Ultrasonic systems transmit ultrasonic energy into a subject and receive reflected ultrasonic energy from the subject. Such ultrasonic systems can process received energy and generate an image for analysis by a user. Accordingly, ultrasonic systems are frequently used in medical diagnostic procedures to provide detailed images of internal organs and body structures. For example, the use of ultrasonic systems allows a surgeon to search for tumors, sparing patients the discomfort and inconvenience of invasive exploratory surgery. Ultrasonic systems are also familiar to many parents as the devices that provided the first pictures of their developing children in-utero.
Such ultrasonic systems generally include a transducer array with a number of individual transducer elements arranged in a predetermined geometry in one or two dimensions. Piezoelectric materials, generally of ceramic or polymeric material, convert between electrical energy and acoustic energy and are often used to form individual transducer elements. A multi-element transducer array is generally formed from a strip of such piezoelectric material, which is then cut to form a row or rows of individual transducer elements.
Ultrasonic systems that use transducer arrays with large numbers of individual transducer elements are generally desirable as providing a large viewing field, a large signal aperture, and/or to provide desired beam forming. Typically, as the density of individual transducer elements of a transducer array increases, so does the image quality produced by a system using that transducer array. However, as the density of the transducer array increases, the pitch of the transducer array, or the longitudinal distance of individual transducer elements, decreases. In conventional transducer arrays, a small transducer array pitch can result in undesirable interference between elements in the form of electrical and acoustic interactions, and image quality can suffer due to such cross-talk. Cross-talk can occur at the transducer and also in transmission circuitry contained in a transducer array head. As a transducer array becomes more dense, so too do connectors providing electrical connections to the transducer array, conductive circuits on printed circuit boards, and other transmission apparatus connected to the array. If the pitch between conductive circuits becomes too small, undesirable electrical cross-talk increases.
Various ultrasonic systems have employed transducer arrays wherein transducer elements are disposed in a two-dimensional configuration. That is, a plurality of transducer elements are disposed along the long or longitudinal axis of the transducer array and a plurality of transducer elements along the width or lateral axis of the transducer array. Such two-dimensional transducer arrays typically assume a configuration in which separate signal transmission path circuits are each coupled to a parallel set of transducer elements. To the inventors' knowledge, such two-dimensional arrays have not been used to address the foregoing transducer element density issues or to provide improved directivity, but rather have been to provide a transducer array configuration adapted for use in particular situations.